The mad scientists at CERN just announced that they trapped antimatter atoms using the aptly named Antihydrogen Laser Physics Apparatus (ALPHA.) Since I can't even pretend to explain how amazing this is, I'll just cheat and quote from the press. (I can't, however, stop hearing the voices in my head saying "It's all fun and games until somebody gets hurt." How long before they make antimatter rayguns?)
From CERN: "Antimatter – or the lack of it – remains one of the biggest mysteries of science. Matter and its counterpart are identical except for opposite charge, and they annihilate when they meet. At the Big Bang, matter and antimatter should have been produced in equal amounts. However, we know that our world is made up of matter: antimatter seems to have disappeared."
From National Geographic: "Theories predict that antimatter particles and matter particles have opposite electrical charges but are otherwise nearly identical. Whenever the matter and antimatter meet, they self-annihilate in a shower of pure energy."